The speciesC. amalonaticus, C. koseri, and C. freundii can use citrate as a sole carbon source. Citrobacter species are differentiated by their ability to convert tryptophan to indole (C. koseri is the only citrobacter to be commonly indole-positive), ferment lactose (C. koseri is a non-lactose fermentor), and use malonate.[2]

Citrobacter shows the ability to accumulate uranium by building phosphate complexes.[3]

C. freundii strains have inducible ampC genes encoding resistance to ampicillin and first-generation cephalosporins. In addition, isolates of Citrobacter may be resistant to many other antibiotics as a result of plasmid-encoded resistance genes.